Materials that have desirable breathability and moisture barrier properties are useful in personal care products such as diapers, incontinence and feminine care articles, where the object is to contain fluids within the product structure while allowing for external air exchange. A traditional means for providing such materials is to incorporate an outer cover having a breathable microporous structure yet which is capable of maintaining liquid barrier properties. These materials typically comprise a laminate or composite of a film layer and an elastic layer (usually made of a nonwoven material). Traditionally, the film layer has been made of a polyolefin or polyurethane material. However, such materials have been limited because they did not provide suitable elastic and breathability properties required for personal care products. Recently, some extensible polyolefins have been developed, but such materials have limited elasticity.
Aperturing polyolefins or similar materials can be done by mechanical or other force applying techniques. Mechanical aperturing tends to create ragged edge holes, whereas blowing agents tend to create smoother holes. Smoother holes are stronger and are more resist to tearing than are ragged edge holes because there are fewer stress points in the film. Mechanical aperturing of polyolefins is possible because the film formed therefrom has sufficient stiffness to prevent substantial deformation of the sheet when a pin or other aperturing force is passed therethrough. For materials such as elastomers that form sheets of greater flexibility than polyolefins, mechanical aperturing has been problematic because the material deforms excessively when punctured, resulting in holes that have poor quality and definition or a material that has compromised mechanical properties.
Breathability can also be achieved by the formation of holes or cells within a film. One method by which this can be achieved is by introducing particles of a material such as calcium carbonate into the extrusion mix. The extruded film encapsulates or forms cells or pockets around the particles. When the film is stretched the pockets elongate to form microholes and/or microtears, through which air can pass. A problem with this technique is that hole definition can be poor because stress is introduced into the microporous area, and, if the particles are irregular in shape, the micropores formed can be of irregular shape and subject to tearing, thereby reducing strength. This technique may not be practicable for forming micropores in materials, such as certain elastomers. Even if micropores could be regularly formed in these materials, conceivably they would collapse or close due to retraction of the polymer when the biasing force or stress is removed.
Elastomers are desirable materials for use in personal care products because their stretch and recovery attributes lend themselves to improved shaping, conformability, and potentially improved functionality, compared to polyolefins. Introducing holes or openings in the form of pores or apertures in elastomers, however, has been a problem because it is difficult to retain the porous structure due to relaxation of the elastomer. It would be desirable to have a process that could form apertures in elastomers and provide predictable aperture definition without appreciably increasing manufacturing cost. It would also be desirable for such an aperturing process to allow for control of hole size, hole distribution and other related properties as a function of stretch or elongation.
Accordingly, it is an object of the present invention to provide a cellular elastomeric composite material which provides an appropriate level of breathability, fluid barrier properties, and elasticity suitable for use in personal care products.
It is yet another object of the present invention to provide a process for forming a cellular elastomer film composite having predictable hole definition, hole distribution and acceptable mechanical properties.
It is a further object of the present invention to provide a composite laminate material comprised of at least one layer of a woven or nonwoven material and a layer of a cellular elastomer film or fibrous material which has pores that are created by adding a cell opening agent to an elastomer polymer and extruding the mixture so that the cell opening agent forms open and/or closed cells in the film produced from the elastomer polymer.
It is yet another object of the present invention to provide a material having a breathable film layer suitable for use as a stretchable top sheet for use in management of body fluids such as menses, blood, urine and runny bowel movement.